16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12472
Comparative dynamics of tea (Camellia sinensis L.) roots under
organic and conventional management systems with special
reference to water use
Mohotti, A. J.1, Damayanthi,M.M.N.2, Anandacoomaraswamy, A.3 & Mohotti, K. M..4
Key words: organic, tea, roots, water use
Abstract
Comparative measurements were carried out in the on-going, long-term organic and
conventional comparison “TRI OR-CON” trial at the Tea Research Institute of Sri
Lanka. The tea was grown organically using tea waste (TW), neem oil cake (NOC),
compost (COM) as soil amendments using IFOAM guidelines, which were compared
with tea grown conventionally (CONV) with recommended synthetic inputs.
Responses of the tea yield, root system and mass volume sap flow were studied.
The tea bushes showed comparable responses between all the treatments, the
differences of which were not statistically significant: They exhibited similar yield, root
distribution, growth, extension rates, mortality, mass volume flow of water and water
use efficiency (WUE). The organically grown (ORG) tea bushes invested more roots in
deeper soil layers than the CONV bushes.
The results showed that in terms of plant growth, managing tea organically is as
equally feasible as managing tea in the conventional manner.
Introduction
Sri Lanka is the pioneer in organic tea production. However, organic systems provide
more management challenges than conventional systems. Organic cultivation is often
blamed for higher cost of production and low productivity, mainly owing to limited
technology available (Peck, 2004). The comparative responses of the tea (Camellia
sinensis L.) shoots in organic and conventional systems have been previously
reported (Mohotti et al., 2001). However, there is very scarce information on the
comparative responses of the tea root system in organic and conventional systems of
tea, with even little information on the comparative studies on water relations.
Therefore, this study was carried out to examine and compare the behaviour of the
root system and study the sap flow of field grown mature tea, grown under organic
and conventional management systems.
1
Plant Physiology Division, Tea Research Institute of Sri Lanka, Talawakele, Sri Lanka, E-Mail
mohottij@yahoo.com
2
Plant Physiology Division, Tea Research Institute of Sri Lanka, Talawakele, Sri Lanka, E-Mail
dnalika@yahoo.com
3
Agronomy Division, Tea Research Institute of Sri Lanka, Talawakele, Sri Lanka, E-Mail
anandacoo@yahoo.com
4
Entomology Division, Tea Research Institute of Sri Lanka, Talawakele, Sri Lanka, E-Mail
mohottik@yahoo.com
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12472
Materials and methods
This study was carried out in the on-going, long-term, organic and conventional
comparison “TRI OR-CON” trial, established at St Coombs estate, Tea Research
Institute, Talawakelle, Sri Lanka (latitude 6o55’, longitude 80o40’, altitude 1382 m amsl)
during January 2004 to September 2006. The long-term average annual rainfall in this
region is 2250mm and maximum and minimum temperature 22.80C and 14.20C.
The experiment consisted of approximately ten year-old tea bushes of the cultivar
DT1, in a land area of approximately 1.6 ha, consisting about 20,000 bushes. Three
treatments were managed organically according to IFOAM guidelines viz. TW, NOC
and COM (TW and COM were given at 2kg per bush and NOC at 500g per bush,
twice a year, which contained N%:P%:K% 2.4:0.4:1.7, 2.8:0.5:1.1 and 1.6:3.7:0.3
respectively). These were compared with tea grown conventionally (CONV), using
recommended inorganic fertilizer and other recommended management practices by
the Tea Research Institute (N:P:K at 270:123:200 kg ha-1 year-1). The treatments were
arranged in a randomised complete block design with four replicates. Two sub-plots
each consisting approximately 25 bushes were separately maintained in each plot for
monitoring yield. The bushes were plucked weekly and a representative sample was
oven dried at 95 oC for extrapolation of yield per ha.
Three experiments were carried out in order to study the root dynamics and water
relations: In the first experiment (January 2004), the distribution of the tea root system
was studied. Soil was sampled in fixed volumes of (3375 cm2) using a soil core
sampler, at different distances from the base of the tea bush and at different depths.
The roots were hand-separated and measurements on the root length and weights
were taken. Soil N, P, K, organic C (OC) and soil moisture (MC) contents were
analyzed using standard methods. Data were statistically analyzed using GLM
procedure in SAS statistical package and the means were separated using Duncan’s
Multiple Range Test.
In the second experiment, root windows that were constructed in 10 bushes in each
treatment, using a plane glass fixed to a metal frame, were used. Root maps were
drawn in two-week intervals, during December 2005 to September 2006. Root growth
rate, extension rate, regeneration and mortality were measured using the root maps.
Data were statistically analyzed using GLM procedure.
In the third experiment, sap flow was monitored using sap flow sensors (Thermal
Logic, USA) using the heat-pulse technique, which was fixed to a data logger, in
November and December 2005. An average rainfall of 114 mm was received during
this period (long-term average is 112mm). Only TW and CONV treatments were
included in the experiment due to practical limitations. Water use efficiency (WUE)
was calculated as the ratio between dry matter accumulation and mass flow per day.
Soil moisture content was measured weekly by drying soil samples at 105 oC. Data
were statistically analyzed using GLM procedure.
Results
The yield and soil nutrient contents were not statistically significant at P=0.05 (data not
shown). Differences were significant with soil OC (at P>0.0013) and probably
resultantly in soil MC (at P>0.0027) during a relatively dry period (in experiment 1,
25.8%, 23.4%, 25.9% and 22.7% in TW, NOC, COM and CONV respectively).
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12472
The root distribution parameters (i.e. root weight, total root length) did not significantly
differ (at P=0.05) between the treatments. The total root (young and mature) fresh
weights were not significant at P=0.05, but when expressed as a percentage of roots
in different depths (Figure 1b), showed that in organic treatments, more roots were
concentrated in the deeper layers of soil (i.e. 37% and 35% in 15-30cm and 30-45cm
depths respectively in overall ORG treatments vs 31% and 31% respectively in
CONV) while in CONV, more roots were concentrated in the topmost layer of soil
(38% as against 29% in overall ORG treatments) (Figure 1b).
a
b
Root fresh weight
Total Root Fresh
Weight (g)
20
15
10
5
0
TW
NOC
COM
CONV
100%
27
27
60% 39
15-30cm
38
39
32
31
34
36
31
COM
CONV
40%
20% 34
0%
TW
30-45cm
32
80%
NOC
0-15cm
Figure 1a: Distribution of tea roots in different soil depths and figure 1b: root
fresh weight as a percentage of the total, in each soil depth.
cm -2)
-1
2.5
2.0
a
1.5
1.0
0.5
0.0
TW
NOC
COM
CONV
Root regeneration (mm week
Root Growth (cm cm -2 area week -1)
Feeder root growth rate (Figure 2a), length, mortality and extension rate (data not
shown) did not significantly differ between the treatments. However, root regeneration
rate (Figure 2b) as measured by the number of root tips at each measurement, was
significantly higher in ORG plants compared with the CONV.
0.035
0.03
b
0.025
0.02
0.015
0.01
0.005
0
TW
NOC
COM
CONV
Figure 2: Growth and regeneration rates of tea roots.
2.5
a
2
1.5
1
0.5
0
TW
CONV
Water Use Efficiency (%)
Average Volume Flow
(L/day)
Sap flow studies showed that the volume flow was slightly higher (not significant at
P=0.05) in the CONV treatment (Figure 3a). However, TW showed higher water use
efficiency (WUE) compared to CONV (Figure 3b). During this study, the soil moisture
content did not differ significantly (34.78% and 34.81% in TW and CONV
respectively).
30
25
20
b
15
10
5
0
TW
Figure 3a: Average volume sap flow and b. water use efficiency.
CONV
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12472
Discussion
The tea bushes grown organically and conventionally showed similar performances in
terms of root growth and yield. These results agree with earlier observations made on
comparisons between organic and conventional systems of young tea (Mohotti et al.,
2001) and some other crops such as apple (Reganold et al., 2000), corn (Lang, 2005),
tomatoes (Mitchell et al., 2007) and soybean(Lang, 2005; Prasad, 2005).
Organically grown tea also seemed to invest on a deeper root system compared to the
conventionally grown tea, as reported earlier by Mohotti et al. (2001) in young tea and
similarly in other crops such as soybean (Prasad, 2005). These differences could also
be seen in the WUE, as the TW exhibited higher WUE than CONV. The volume sap
flow was comparable in both CONV and TW. The results also show that the plants in
organic systems use the resources more usefully than the CONV systems. Repeating
the sap flow studies during a dry season can be suggested. In this study, organic
cultivation did not change the soil nutrient content, but improved the organic carbon
content in soil. Resultantly, during dry periods organically managed soils held more
moisture.
Conclusions
The study emphasizes that organically and conventionally grown tea exhibit similar
growth performances, in terms of the responses of the root and shoot systems. This
shows the feasibility of growing tea organically, without affecting the yield or plant
performance.
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